The objectives of the proposed research are to study the metabolism of selected xenobiotic chemicals in fish and to determine the functional significance of these pathways. Attention will be focused on the disposition and metabolism of chemicals which are current environmental problems, namely the polychlorinated biphenyls (PCB's), polycyclic aromatic hydrocarbons and chlorinated phenols such as pentachlorophenol. In addition to determining the persistance and identifying the metabolites of these chemicals, the effect of metabolism on their toxicity will be studied. If biotransformation of these compounds in fish leads to less toxic compounds and the reactions proceed at significant rates, blockade of their metabolism by known specific inhibitors would be expected to increase the acute toxicity (LC 50) of the compound in question. On the other hand, if these biotransformation enzymes are inducible as are the mammalian microsomal enzymes, pre-exposure of fish to inducing agents may be expected to decrease the toxicity of the compound being studied. The information gleaned from these biotransformation studies may lead to the mechanisms of species selectivity of many water borne pollutants in addition to providing data necessary for residue analysis of metabolites of foreign compounds as well as the parent molecule. BIBLIOGRAPHIC REFERENCES: Melancon, M. and Lech, J.J.: Isolation and identification of a polar metabolite of tetrachlorobiphenyl from bile of rainbow trout exposed to 14C-tetrachlorobiphenyl. Bull. Env. Cont. and Toxicol. 15: 181-188, 1976. Statham, C.N. and Lech, J.J.: Studies on the mechanism of potentiation of the acute toxicity of 2,4-D n-butyl ester and Bayer 73 in rainbow trout by carbaryl. Toxicol. Appl. Pharmacol. 36: 281-296, 1976.